1. Technical Field
The present disclosure relates to a sulfide solid electrolyte material having high moisture resistance, and an electrochemical device containing this material.
2. Related Art
A lithium ion secondary battery has high capacity per weight or volume, so that it has been widely used in, for example, mobile devices. Research and development have been actively conducted on the use of lithium ion secondary battery in, for example, the application of electric vehicles that requires higher battery capacity.
A lithium ion secondary battery mainly includes a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.
In most cases, the lithium ion secondary battery uses a liquid electrolyte containing a flammable organic solvent. The secondary battery has therefore a safety mechanism for suppressing an increase in temperature due to short circuit. Moreover, the secondary battery takes structural countermeasures for preventing the electrolyte leakage. Thus, increasing the size and capacity of the lithium ion secondary battery leads to an increase in the need of the countermeasures.
On the other hand, research has also been conducted on an all-solid lithium ion secondary battery with a solid electrolyte. This secondary battery does not contain any flammable organic solvent in the electrolyte. Therefore, since this secondary battery can drastically solve the safety problems of the conventional batteries, this secondary battery has been extensively studied.
In recent years, development has been advanced on materials with a potential of 5 V or more relative in lithium metal reference to improve the capacity of the lithium ion secondary battery. In a lithium ion secondary battery containing a liquid electrolyte, however, the electrolyte has a narrow potential window, and may be thus decomposed when the battery is in operation. In contrast, a solid electrolyte with a wide potential window has advantages in that the electrolyte can be prevented from decomposing and can impart high capacity to the lithium ion secondary battery.
Materials of the solid electrolyte include organic materials, for example, an ionic conductive polymer material such as polyethylene oxide, and inorganic materials, for example, a solid oxide electrolyte material and a sulfide solid electrolyte material. The solid electrolyte containing any of those materials has lower lithium ion conductivity than the liquid electrolyte and therefore may be inferior in output characteristics. However, the sulfide solid electrolyte materials developed in recent years exhibit high ion conductivity as high as that of the liquid electrolyte. For this reason, the realization of the all-solid lithium ion secondary battery with high output has been expected (see JP-A-2007-273214 and JP-A-2010-199033).